1. Field of the Invention
The invention relates to organopolysiloxane compositions crosslinkable by condensation reaction, more particularly to one-component, filler-containing organopolysiloxane compositions which crosslink under the influence of moisture and which crosslink to elastomers with elimination of carboxylic acids such as acetic acid.
2. Description of the Related Art
One-component silicone rubber mixtures which undergo vulcanization to elastomers at room temperature (RTV1 compositions) on ingress of water, and which are storable in the absence of water, are known. These products are used in large quantities, for example, as joint-sealing compositions in the construction industry. The profile of properties requires a multitude of product features for the particular end use that are necessary, in order that the paste can be processed effectively, for rapid and complete curing, and for its function to be fulfilled durably in the vulcanized state.
The basis of these RTV1 mixtures are polydiorganosiloxanes, terminated either with OH groups or with silyl groups which carry hydrolyzable groups. Through the chain length of the polymers and through the fillers used it is possible to exert influence over key properties of the RTV1 mixtures. In sealing applications where the elastic joint is subject to considerable movement, accommodation of movement, in particular, is an important parameter. For the durable fulfillment of function, it is necessary that this ability to accommodate movement remains stable—it must not, for example, go down as a result of severe shrinkage.
Influencing variables for the accommodation of movement are, in particular, the chain lengths of the polymers and the fillers used. Greater chain length enhances accommodation of movement; reinforcing fillers lower it in conjunction with an increasing modulus. For economic and technical reasons, however, only a limited range of polymer chain lengths are available for the production of RTV1 mixtures. Greater chain lengths lead to very high viscosities of the polymers, and so the application-ready products are more difficult to process on account of the viscosity, which is high. Compensating for this high viscosity by means of plasticizers leads to increased volatility, and therefore to a greater loss of weight, with adverse consequences for the fulfillment of function, particularly with regard to the requirement of high accommodation of movement. Consequently, fillers offer one option for adjusting the properties. There are, however, certain restrictions on the selection of the fillers, especially in the case of preparations which crosslink with elimination of carboxylic acids, such as acetic acid.
For example, JP 10-316858 and U.S. Pat. No. 5,938,853 A describe the use of coated chalks in order to prevent the release of CO2 due to the reaction with the acetic acid eliminated from the acetoxysilanes with the carbonate. As a result of working in a mixer or kneading apparatus, however, the coating may be damaged, and there is release of CO2, leading to the inflation of cartridges.
DE 34 39 745 A1 describes, alternatively, the use of silicates which have been surface-pretreated beforehand. Silicates are slightly reinforcing fillers, resulting in increasing modulus and falling declining accommodation of movement.
The use of kaolin as a filler for acetic compositions is described in WO 2009/080266 AI. Here again, there is a considerable increase in the modulus of the sealants, leading to increased flank exposure in joint applications. High accommodation of movement is therefore likewise not realizable.
Further fillers which are compatible with acetic compositions, such as quartz powders, for example, likewise result in low accommodation of movement.